1. Field of the Invention
The present invention relates to a portable electrocardiograph capable of easily measuring and storing electrocardiographic waveforms.
2. Description of the Background Art
Generally, for diagnosing ischemic cardiomyopathies such as angina pectoris and myocardial infarction, an electrocardiograph of the patient is used. Known electrocardiographs for measuring electrocardiographic waveforms include stationary electrocardiographs and portable electrocardiographs.
Stationary electrocardiographs are generally found in medical institutions such as hospitals, and they measure waveforms by attaching electrodes to the body of a patient who lies on a bed or the like. The use of a stationary electrocardiograph is advantageous because it is able to measure various electrocardiographic waveforms (such as P waveform and QRS waveform) very precisely. However, stationary electrocardiographs suffer from the fact that, in many cases, the events they are seeking to monitor have past and therefore a proper diagnosis is not possible.
Portable electrocardiographs generally include Holter electrocardiographs and event-type electrocardiographs. Holter electrocardiographs are used to continuously measure and store electrocardiographic waveforms using electrodes which are attached to the body of a patient on a continual basis over a period of days. Event-type electrocardiographs operate by having electrodes applied to the body when a subjective symptom to be measured such as palpitation or pain occurs.
Holter electrocardiographs are very reliable for measuring abnormal waveforms. However, since this method requires that the electrodes remain attached for a period of days, patients are greatly inconvenienced and subject to a great deal of pain and discomfort.
The event-type electrocardiographs generally fall into one of two categories. A first category is comprised of devices which use electrodes which are always in contact with a predetermined region of the body. A second category is comprised of devices which are applied to the body when a subjective symptom to be measured occurs, and the test subject himself/herself makes an electrode comes in contact with the body.
In the first category of event-type portable electrocardiographs, like the Holter portable electrocardiograph, a state where the electrode is always in contact with the body has to be maintained, so that the test subject is inconvenienced. In contrast, in the second category of event-type portable electrocardiographs, it is sufficient to attach the electrode to the body when necessary, so that the portable cardiograph is very easy-to-use for the test subject.
Within the second category of event-type portable electrocardiographs, devices using various configurations of electrodes and body surfaces have been proposed.
For example, Japanese Patent Laying-Open No. 61-41438 discloses, as shown in FIG. 20, a portable electrocardiograph 100D having a configuration in that a display 150 is provided on a front face 102 side of a housing 101 of an electrocardiograph monitor and three electrodes 110, 120 and 130 to be attached to the body of a test subject are provided on a rear face 103 side. Measurement is carried out by making the three electrodes 110, 120 and 130 come into contact with the chest of the test subject.
Japanese Utility Model Laying-Open No. 3-91304 discloses a portable electrocardiograph 100E having a configuration in that, as shown in FIGS. 21A and 21B, the electrode 110 is attached to the front face 102 of the housing 101, a supporting member 191 extending from the top of the housing 101 along the rear face 103 side of the housing 101 is attached to a top face 104 of the housing 101 by using a hinge 192, and the electrode 120 is provided on the surface of the supporting member 191. At the time of measurement, the supporting member 191 is swung (see FIG. 21C), an electrode formation face of the supporting member 191 and the front face 102 of the housing 101 are arranged to be almost in the same plane, and electrocardiographic waveforms are measured in a state where the two electrodes 110 and 120 are in contact with the chest of the test subject.
Japanese Utility Model Laying-Open No. 3-91305 discloses a portable electrocardiograph 100F having a configuration in that, as shown in FIGS. 22A and 22B, the electrode 110 made of electroconductive rubber is provided on the front face 102 of the housing 101 and the electrodes 120 and 130 are provided on a right side face 106 and a left side face 107, respectively, of the housing 101. At the time of measurement, the test subject holds the housing 101 from the rear face 103 side of the housing so as to make contact with the electrodes 120 and 130 provided on both of the side faces 106 and 107 and makes the electrode 110 provided on the front face 102 come into contact with the chest of the test subject to measure electrocardiographic waveforms.
Japanese Patent Laying-Open No. 2003-144403 discloses a portable electrocardiograph 100G having a configuration in that, as shown in FIG. 23, a negative electrode 110 and a neutral electrode 130 are provided on the top face 104 and a bottom face 105, respectively, which are opposite surfaces of the housing 101 having an almost rectangular parallelepiped shape, and a positive electrode 120 is provided on the left side face 107 which is a curved surface adjacent to the faces on which the negative electrode 110 and the neutral electrode 130 are provided. On the front face 102 of the housing 101, the display 150 for displaying a measurement result and an operation button part 140 in which various operation buttons typified by a power source button 141 for turning on the power source are provided.
At the time of measurement, the test subject himself/herself holds the negative electrode 110 and the neutral electrode 130 provided on the top face 104 and the bottom face 105, respectively, from the rear side of the housing 101 by his/her right hand and makes the electrode provided on the left side face 107 of the housing 101 come into contact with his/her chest to measure electrocardiographic waveforms.
In such a portable electrocardiograph having an electrode on the outer surface of the housing, the contact portion between the electrode and the body has to be kept stable throughout the entire measurement period, which may be tens seconds. In the case where stable contact is not maintained, the measured electrocardiographic waveforms are disturbed and cannot be measured with precision.
In the conventional portable electrocardiographs, the contact between the electrode and the measured body is generally maintained by manually pressing the electrocardiograph main body against the measured body at the time of measurement. More specifically, the wrist of the holding hand, forearm, elbow or the like is pressed against the body of the user, thereby preventing the holding hand from being moved during measurement and stably maintaining the contact between the electrode and the body. This point will be described more specifically with reference to portable electrocardiograph 100G disclosed in Japanese Patent Laying-Open No. 2003-144403.
FIG. 24 is a diagram showing a measurement posture to be taken by the test subject at the time of measuring electrocardiographic waveforms by using the portable electrocardiograph 100G disclosed in Japanese Patent Laying-Open No. 2003-144403. As shown in FIG. 24, upon measurement, a test subject 200 presses the wrist portion of a forearm 220 against a portion of the right side of the body while holding the portable electrocardiograph 100G with his/her right hand 210 while also contacting the positive electrode 120 provided on the left side face 107 of the housing 101 of the portable electrocardiograph 100G with the skin of a left lower part of a chest 250. While maintaining contact for tens of seconds, electrocardiographic waveforms are measured.
FIG. 25 shows a state where the portable electrocardiograph 100G is held by the right hand 210. As shown in FIG. 25, the test subject 200 holds the housing 101 while covering the rear face side of the housing 101 with the palm so that the front face 102 of the portable electrocardiograph 100G faces upward. The housing 101 is held by lightly bending a forefinger 212, a middle finger 213, a ring finger 214 and a little finger 215 of the right hand 210 so that any or all of them come into contact with the negative electrode 110 provided for the top face 104 of the housing 101. A thumb 211 extends along the bottom base 105 of the housing 101 to hold the housing 101 while being in contact with the neutral electrode 130 provided on the bottom face 105. The wrist portion of the right hand 210 is pressed against the right side of the body and the right hand 210 is fixed so that the positive electrode 120 formed on the left side face 107 of the housing 101 is not apart from the body.
In the case of measuring the electrocardiographic waveforms in such a measurement posture, if the wrist of the right hand is covered with cloth, the right hand and the right side of the body are not in direct contact with each other. Consequently, a measurement circuit in this portion (an electric circuit formed in the body from the positive electrode to the negative electrode) can be prevented from being short-circuited, so that electrocardiographic waveforms can be measured with high precision. In the case where the test subject does not wear cloth or wears cloth such as a short-sleeve shirt with which the wrist is not covered, the right hand and the right side of the body come into direct contact with each other. In this portion, the measurement circuit is short-circuited. Consequently, the measurement circuit does not cross the heart, so that electrocardiographic waveforms cannot be measured with precision. In such a state, it is difficult to detect ischemic cardiomyopathies of an early stage and the object itself of measuring electrocardiographic waveforms may be lost.
However, if the wrist is not fixed by pressing the right hand against the right side of the body, the contact between the electrode and the body becomes unstable and a large disturbance occurs in the measured electrocardiographic waveforms. In many cases, the test subject uses a portable electrocardiograph when he/she feels palpitation, pant, dizzy or the like. In such a state, it is very difficult to stably maintain the contact between the electrode and the body and the body moves inevitably at the time of measurement.